1. Field of the Invention
The present invention relates to a method of and apparatus for coating a wafer with a photoresist. More particularly, the present invention relates to minimizing the amount of photoresist necessary to coat a wafer supported for rotation beneath a nozzle from which the photoresist is sprayed.
2. Description of the Related Art
The semiconductor device fabrication process, in which wafers are processed into semiconductor devices having electrical characteristics, invariably includes many steps of coating the wafer with a photoresist. The photoresist is used for masking the wafer during various processes, including, among others, an etching process, an ion implantation process and a metalization process.
The photoresist is applied to the wafer by a spin coater. The spin coater comprises a pumping part for withdrawing photoresist from a supply source and a coating part for spraying the photoresist onto the wafer.
The pumping of the photoresist from the supply source is carried out using a pressurized nitrogen method. Furthermore, as shown in FIG. 1, the coating part includes a nozzle 14 fixed at a specific location over the wafer 12. The wafer 12 is mounted on a rotary chuck 10. The photoresist is sprayed from the nozzle 14, and the resulting thickness of the photoresist on the wafer 12 is dependent on the rate of rotation of the rotary chuck 10.
As shown in FIG. 1, the photoresist sprayed toward the upper central portion of the wafer 12 spreads toward the periphery of the rotating wafer. This is how the periphery of the wafer 12 is coated with the photoresist.
However, in the prior art as described above, 7 ccxcx9c9 cc of photoresist is sprayed from the nozzle 14 to provide a layer of photoresist on a wafer. This amount exceeds the amount which is actually necessary (less than 1 cc) for forming a layer of photoresist of the required thickness on the wafer.
That is, too much photoresist is sprayed on the wafer meaning that much of the photoresist is wasted. Such an economic loss is magnified considering the post-use treatment of the photoresist necessary to respond to environmental concerns.
Therefore, there is a great demand for a method of spraying photoresist which avoids wasting the photoresist.
An object of the present invention is to provide a photoresist coating apparatus and method wherein the photoresist is not wasted, i.e., which minimizes the amount of photoresist necessary to coat the wafer.
To achieve these and other objects, the present invention provides a coating apparatus that includes a linear driving mechanism operatively connected to the spray nozzle so as to move the nozzle in a radial direction of a wafer chucked to a rotary chuck. A variable speed motor is operatively connected to the rotary chuck for rotating the chuck. A controller adjusts the speed of the motor, based on the location of the nozzle, while the nozzle is moved by the linear driving mechanism in a direction from the peripheral edge of a wafer toward the center of the wafer.
The controller is configured such that the rotational speed of the motor is gradually increased linearly or non-linearly while the nozzle scans the wafer.
The photoresist coating method similarly includes steps of chucking a wafer to a rotary chuck; subsequently rotating the chuck at an initial speed; moving the spray nozzle radially across the wafer in a direction from the peripheral portion of the wafer toward a central portion of the wafer, to spray the wafer with photoresist; and increasing the speed at which the chuck is rotating while the nozzle is moved from the peripheral edge of the wafer toward its center.